It is known that catalysts formed by combining an organometallic compound of a metal of Groups IIA, IIB and IIIA of the Periodic Table with a halide of vanadium or titanium are useful for polymerizing mono 1-olefins at low pressures and low temperatures to form resinous polyolefins. In preparing such catalysts, particularly suitable organometallic compounds are the alkyl, especially the lower alkyl compounds, of the metals of Groups IIA, IIB and IIIA, such as aluminum, zinc, cadmium and beryllium. Organometallic compounds in which the metal is attached to cycloalkyl radicals of 3 to 7 carbon atoms or aromatic radicals such as phenyl, as well as halogenated compounds such as dialkyl aluminum chlorides, are also suitable.
Some of the titanium and vanadium halides useful in preparing the aforementioned catalysts are the titanium and vanadium tetrachlorides, as well as the oxyhalides of such metals including vanadium oxychloride.
As specific examples of suitable organometallic compounds useful in forming the aforementioned catalysts can be mentioned the dialkyl cadmiums such as diethyl-cadmium, dimethylcadmium and diisobutylcadmium, the dialkylzincs such as diethylzinc and dibutylzinc, the trialkylaluminums and dialkylaluminum hydrides such as diisobutylaluminum hydride, diethylaluminum hydride, trimethylaluminum, triethylaluminum, tripropylaluminum, triisobutylaluminum and diethylaluminum chloride, the cycloalkyl metal compounds such as tricyclohexylaluminum, and the aryl metal compounds such as diphenylcadmium and dinaphthylzinc. The alkyl group on such compounds is advisably a lower alkyl and particularly such a group having 1 to 4 carbons.
These catalysts are conveniently produced by reacting the organometallic compound with the metal halide in the presence of a hydrocarbon solvent such as isooctane, n-heptane, xylene or benzene. The molar ratio between the organometallic compound and the halogenated metal can be varied within wide limits. A ratio of about 0.25 to about 4 mols of halogenated compound, such as titanium or vanadium tetrachloride, to one mol of the organometallic compound is suitable. A typical catalyst system could be composed of triisobutylaluminum and titanium tetrachloride combined in an equimolar ratio.
The above-described catalysts and processes are useful for polymerizing mono 1-olefins such as ethylene, propylene, butene-1, pentene-1, hexene-1, 4-methyl-1-pentene, vinylcyclohexane, and styrene.
Prior art processes have been described in which the transition metal halide is deposited on a carrier such as bentonite, pumice, kieselguhr, calcium, barium or strontium phosphate, zinc oxide, calcium oxide, or nickel oxide, and the base supported catalyst components mixed with the above-described co-catalysts to polymerize a mono 1-olefin. Such catalysts have only moderate productivities based on the total catalyst mixed, with the result that the catalyst components must be removed before the product polymer can be utilized. Productivities have been improved by the use of magnesium compounds such as magnesium oxide, magnesium sulfate, magnesium halides and basic magnesium carbonate as carriers for the Ziegler-type catalysts in the polymerization of ethylene, for example. These and other similar magnesium compounds when treated by conventional processes with a transition metal halide are believed to chemically react through their residual hydroxyl groups according to the following equation: EQU ClMg--OH + TiCl.sub.4 .fwdarw. ClMg--O--TiCl.sub.3 + HCl
The reaction forms hydrocarbon insoluble products. A serious disadvantage of these prior art processes is that the polymerization reaction must be conducted for extremely long time periods, indicating extremely low productivity, to obtain a polymer product wherein the catalyst concentration is sufficiently low so as not to require a separate catalyst removal step.
Accordingly, an object of the invention is to provide a mono 1-olefin polymerization process employing a Ziegler-type catalyst wherein productivity of the catalyst is substantially improved.
Another object of the invention is to provide ethylene and propylene polymerization processes employing Ziegler-type catalysts wherein productivity of the catalysts is substantially improved.
Yet another object of the invention is to provide an improved mono 1-olefin polymerization process employing a Ziegler-type catalyst wherein the transition metal halide employed comprises titanium tetrachloride.
Other objects, advantages and features of the invention will be readily apparent to those skilled in the art from the following description and appended claims.